Cutting elements, such as shear cutter type cutting elements used in rock bits or other cutting tools, typically have a body (i.e., a substrate) and an ultra hard material. The ultra hard material forms the cutting surface of the cutting element, and the substrate typically attaches the ultra hard material to the cutting tool. The substrate is generally made from tungsten carbide-cobalt (sometimes referred to simply as “cemented tungsten carbide,” “tungsten carbide” or “caarbide”). The ultra hard material layer is a polycrystalline ultra hard material, such as polycrystalline diamond (“PCD”), polycrystalline cubic boron nitride (“PCBN”) or thermally stable product (“TSP”) such as thermally stable polycrystalline diamond. The ultra hard material provides a high level of wear and/or abrasion resistance that is greater than that of the metallic substrate.
PCD is formed by a known process in which diamond crystals are mixed with a catalyst material and sintered at high pressure and high temperature. The catalyst material may be mixed into the diamond powder prior to sintering and/or may infiltrate the diamond powder from an adjacent substrate during sintering. The high pressure high temperature sintering process (“HPHT sintering”) creates a polycrystalline diamond structure having a network of intercrystalline bonded diamond crystals, with the catalyst material remaining in the voids or gaps between the bonded diamond crystals.
The catalyst material facilitates and promotes the inter-crystalline bonding of the diamond crystals. The catalyst material is typically a solvent catalyst metal from Group VIII of the Periodic table, such as cobalt, iron, or nickel. However, the presence of the catalyst material in the sintered PCD material introduces thermal stresses to the PCD material when the PCD material is heated, for example by frictional heating during use, as the catalyst typically has a higher coefficient of thermal expansion than does the PCD material. Thus, the sintered PCD is subject to thermal stresses, which limit the service life of the cutting element.
To address this problem, the catalyst is substantially removed from the PCD material, such as by leaching, in order to create TSP. For example, one known approach is to remove a substantial portion of the catalyst material from at least a portion of the sintered PCD by subjecting the sintered PCD construction to a leaching process, which forms a TSP material portion substantially free of the catalyst material. If a substrate was used during the HPHT sintering, it is typically removed prior to leaching.
After the TSP material has been formed, it can be bonded onto a new substrate in order to form a cutting element. During this process, called the “re-bonding process,” the TSP material and substrate are subjected to heat and pressure. An infiltrant material (such as cobalt from the substrate) infiltrates the TSP material, moving into the pores (i.e., the voids or interstitial spaces) (collectively or individually referred to herein as “pores”) between the bonded crystals, previously occupied by the catalyst material. The infiltration of this infiltrant material from the substrate into the TSP layer creates a bond between the TSP layer and the substrate. The re-bonded TSP layer may be partially re-leached to improve the thermal stability, such as at the working surface of the TSP layer.
Existing TSP cutting elements are known to fail prematurely due to insufficient infiltration of the infiltrant material into the TSP layer during the re-bonding process, leading to residual porosity in the re-bonded TSP layer. As explained above, when the PCD material is leached to form TSP, the catalyst material in the PCD layer is removed from the pores between the diamond crystals. If these pores are only partially infiltrated or not properly infiltrated during the re-bonding process, the empty pores can weaken the bond and create structural flaws. This partial infiltration makes the TSP cutters vulnerable to cracking during finishing operations such as lapping and grinding. Partial infiltration also makes re-leaching more difficult, and weakens the bond between the TSP layer and the substrate. Accordingly, there is a need for a method for forming TSP material that facilitates infiltration during re-bonding, and improves the thermal characteristics and operating life of the material.